The present invention relates generally to thermal imaging systems and, more particularly, to an infrared sensor calibration system for determining exposure settings, non-uniformity correction temperatures and calibration temperatures to use at close range for measurement of high temperature targets at long range.
Infrared (IR) sensor systems are commonly used to generate thermal images of a scene being viewed. For example, IR sensor systems may be used in long-range detection and tracking of various targets including missiles and aircraft. The IR sensor produces a radiometric IR signature which generally represents the amount of infrared energy emitted by the tracked object in comparison to objects in the background.
For imaging an object, it is necessary that the range of temperatures emitted by the tracked object fall within the dynamic range of the IR sensor system which may comprise an IR camera and/or spectro-radiometer. Prior to imaging, it is necessary to calibrate for the specifications of a given IR sensor, a given target spectral signature and a given atmospheric model to ensure that there is no instrument saturation during long-range target imaging.
Prior art methods of calibrating IR sensor settings are typically performed using a relatively slow, iterative process. For example, a field test engineer may estimate average sensor response, average target signature and average path (i.e., atmospheric) transmittance. The test engineer may then calculate signal levels at the sensor estimating calibration temperatures and then manually iterating using spreadsheets and/or calculators to find sensor integration times. In another prior art method, a test engineer may pick integration times, guess the corresponding temperature ranges for the integration times and then calibrate the infrared sensor and hope that the image does not saturate.
Unfortunately, because prior art methods of calibrating IR sensor settings are performed manually, they may be subject to inaccuracies. For example, IR camera settings may be predicted using rules of thumb that may not be accurate for a given IR sensor, target spectral signature and atmospheric model. The result may be a poor estimation of the IR sensor settings.
Another drawback of prior art calibration methods is related to the relatively short period of time during which certain thermal imaging events occur. For example, during a missile launch, the thermal imaging may be on the order of a few minutes or less. Because of the short imaging window for missile launches and other short-duration events, there is insufficient time to adjust camera settings. Incorrect system settings may result in a risk of saturation and poor thermal signature measurement. Poor quality measurements as a result of incorrect IR sensor settings may necessitate the re-running of the thermal imaging which may be costly and time-consuming.
As can be seen, there exists a need in the art for an IR calibration system and method that is capable of predicting various IR sensor settings for use in radiometric signature measurement of long-range, high-temperature targets. Furthermore, there exists a need in the art for an IR calibration system and method that rapidly and accurately predicts such IR sensor settings for calibration purposes.
Additionally, there exists a need in the art for an IR calibration system and method which allows for setting radiometric measurement instrumentation to span target thermal energy. Finally, there exists a need in the art for an IR calibration system and method capable of reducing the risk of saturation and resulting bad signature measurements and time and cost associated therewith.